338 Brown. — Studies in the Physiology of Parasitism. I. 
It appears, therefore, that by none of the methods above described was 
it possible in any way to obtain any separation of the macerating and lethal 
actions of the extract. 
G. Relation of Activity of Extract to certain 
Chemical Substances. 
Acidity of Extract. 
The standard extract shows a weak acid reaction. With any of the 
usual indicators, the neutral point is not sharply defined, so that the acidity 
fl 
can only be measured approximately. With phenolphthalein, was es¬ 
tablished as upper limit of acidity ; with neutral red the acidity was given as 
78 o t0 200* ^ ur * n £ the process of neutralizing the latter indicator changes 
continuously from red to yellow. This would indicate that the acids 
present are of a very weak or of a polybasic nature. 
Effect of varying the Acidity on the Activity of the Extract. 
(i) Diminution of Acidity. As the acidity of the extract is diminished, 
the activity remains unaltered up to a certain point, when it falls sharply to 
zero. In alkaline solution the extract has no activity. The following table 
will serve to illustrate the sharp effect produced on neutralization of the 
extract : 
Indicator in each case = i drop of per cent. Solution of Neutral Red. 
20 drops of Alkali solution = i c.c. 
No. 
Extract. 
Indicator. 
Acidity. 
Time to 
decompose 
turnip disc. 
1. 
5 c.c. Ext. + 6 drops water 
red 
n 
200 
18 min. 
2. 
5 c.c. Ext. + 4 
a 
+ 2 drops 
N 
— NaOH 
10 
grading 
3 » 
1000 
18 min. 
3 - 
5 c.c. Ext. + 3 
a 
)> 
+ 3 
a 
a 
continuously 
2 n 
1000 
20 min. 
4 - 
5 c.c. Ext. + 2 
>} 
if 
+ 4 
a 
a 
into 
n 
1000 
35 min. 
5 - 
5 c.c. Ext. + 1 
a 
)> 
+ 5 
a 
>> 
[clear, permanent 
0 
100 min. 
6. 
5 c.c. Ext. + 0 
>> 
+ 6 
a 
„ 
( yellow 
— alk. 
1000 
>20 hrs. 
In the case of (6) the disc remained coherent and quite alive 
(i.e. turgid) after 20 hours. In the remainder, death of the cells followed in 
the usual way. This shows tha.t the lethal principle of the extract reacts as 
